1. Field of Invention
This invention relates generally to electronic systems and more specifically to electronic systems using optical fibers to carry data between components of the system.
2. Discussion of Related Art
Many types of electronic systems are known. Common examples of electronic systems are computers, routers and telecommunications switches. Complex electronic systems have long been built as subassemblies that are then integrated into an overall system. Integration requires that data be passed between subassemblies.
Traditionally, integration of subassemblies has included making connections for electrical signals to carry data between the subassemblies. In some systems, printed circuit boards, sometimes called backplanes, are used to carry electrical signals between subassemblies. Backplanes are usually built as printed circuit boards. Conductive traces within the board carry electrical signals and electrical connectors attached to the board allow subassemblies to be connected to those traces.
In some instances, subassemblies are also built on printed circuit boards, called daughter cards. The conductive traces on the daughter cards interconnect electronic components mounted on the board. The traces also connect those components to connectors on the daughter card. The daughter card connectors mate with backplane connectors to allow the electronic circuitry on the daughter card to pass information in the form of electrical signals through the backplane to other subassemblies connected to the backplane. Where interconnections are made through a backplane, all of the subassemblies to be connected together are usually mounted in one housing.
In other instances, some electronic systems are made up of subassemblies that are contained in separate housings. The system might be too big to fit in a single enclosure or might require subassemblies located in physically separate locations. For example, data storage farms are made of interconnected storage units because it is likely that one unit containing all the necessary circuitry would be too large to easily fit within a single housing. Routers and switches in networks are made as separate pieces to allow the network to span a wide geographic range. A system also might be manufactured as separate components as a matter of convenience. For example, a system might be made from modules to allow systems of many different sizes to be constructed by integrating different numbers of modules.
Where systems are assembled from separate components, cables are often used to interconnect the components. Electronic components that are intended to be integrated into a much larger system often have “panels” or “bulkheads” to which cables interconnecting the subsystems can be connected.
Often, the panel on a subassembly contains electrical connectors. Inside the subassembly, these connectors might be connected to backplanes or daughter cards or otherwise tied into the system. On the outside of the subassembly, the connectors are shaped to receive connectors on the ends of cables. In this way, cables can be plugged into panels to interconnect the subassemblies.
As electronic systems became more powerful, the data rate between subassemblies increased. To carry more data, optical interconnections were often used. Rather than transmit data as electrical signals on conductors, optical interconnections transmit data as modulated light in a structure that acts as an optical waveguide—often an optical fiber. To facilitate the interconnection of subassemblies using optical fibers, optical connectors have been developed. Both backplane/daughtercard and panel type optical connectors are known.
Several problems exist with optical interconnections that do not exist with corresponding electrical connectors. One particular problem is that the optical fibers must be aligned with much higher precision than electrical conductors for optical connectors to reliably transmit signals.
Alignment in optical connectors is often achieved through the use of several levels of alignment mechanisms. At the most precise level, the fiber in both halves of the connector is held in ferrules. Ferrules are precision manufactured components that contain alignment features.
Early designs used single fiber ferrules. These ferrules are generally cylindrical, with the outer surface of the cylinder being the alignment feature. Alignment of the fibers was achieved by inserting the ferrules into opposite ends of a sleeve. The sleeve was also a precision component, ensuring that the faces of the ferrules would align inside the sleeve. Often, the sleeve was incorporated into an adapter and connectors holding the ferrules were plugged into both sides of the adapter.
Multi-fiber ferrules have also been developed, such as the MT ferrule. Alignment features in these ferrules include posts and holes. The fibers held in the ferrules are aligned when the posts of one ferrule are in the holes of another ferrule.
However, for the ferrules to align the fibers as two connectors are mated, the ferrules must first be aligned such that the posts engage with the holes. This level of alignment is often provided through a connector housing. The connector housings have features that, when interlocked, ensure that the ferrules will be aligned with sufficient precision.
Another level of alignment is often used to ensure the housings line up and also to hold the connectors together when mated. A device that provides this level of alignment is also called an adapter. In a simple form, an adapter can be a sleeve into which two connectors can be inserted from opposite directions. The sleeve forces the connector housings into alignment when they come together in the center of the sleeve. Latching features can be incorporated into the sleeve to hold the connector housings together.
An example of an optical connector system can be found in U.S. patent application Ser. No. 10/243,458, filed Sep. 13, 2002, entitled Techniques for Forming Fiber Optic Connections in an Modularized Manner, now U.S. Pat. No. 6,832,858; U.S. Patent Application 2003/0044127 filed Jul. 16, 2002 entitled Modular Fiber Optic Connection System; U.S. patent application Ser. No. 10/326,480 entitled Latch and Release System for a Connector, filed on Dec. 20, 2002, by Roth, et al., now U.S. Pat. No. 6,776,645, all of which are hereby incorporated by reference in their entireties.
The above referenced patents and applications describe optical interconnection systems that use multi-fiber ferrules, housings and adapters for alignment. The adapters used for the backplane/daughter card interconnection in some of the examples have several sleeves tied together in a row. Though ferrules that can simultaneously align multiple fibers are known, forming several housings into a connector assembly allows even more connections to be made simultaneously for applications that require many connections.
Despite the development of multi-fiber ferrules, single fiber ferrules are still in use. Not all electronic systems require large numbers of optical fiber interconnects to be made at one time. A particular system simply might not require an exchange of a sufficiently large amount of data to justify a multi-fiber interconnect. And, single fiber interconnects often have different performance characteristics than multi-fiber interconnects. Single fiber connectors are more likely to be made with multimode fiber, which is larger than single mode fiber traditionally used in multi-fiber interconnects. Multimode fibers tend to exhibit less loss at mating interfaces than smaller single mode fibers.
For this reason, it will sometimes be preferable to create a connector with multiple single fibers for ferrules than to use one multifiber ferrule. There are tradeoffs between use of single fiber interconnection and multi-fiber interconnections, making some types more suitable for certain applications and others more suitable for other applications. Consequently, suppliers of optical fiber interconnection systems are required to stock or build many types of components to be able to meet the needs for any particular system.
We have recognized a significant advantage can be obtained by providing components of an optical interconnection system that can be flexibly assembled into many different configurations.